Hi shyding,
Here is a thread with an example using C# to call the REST API exposed by rclone rcd
:
https://forum.rclone.org/t/c-code-for-rclone-copy/33990/2
A similar approach can be used from Java.
PS: I suggest getting some hands-on experience with rclone rc/rcd before moving on to librclone having a similar interface.